THE GEOLOGY OF THE DISTRICT 47 



Wirksworth are of more than antiquarian interest. Fluor spar, barytes 

 and calcite are the normal gangues and the ' Blue John ' variety of fluor 

 from Castleton takes pride of place as a Derbyshire mineral specimen. 

 Millclose Mine in Darleydale has been worked continuously since 1861 

 and though other mines are worked intermittently it would appear that 

 most of the ore above water level has been extracted. To-day the 

 abandoned mines and natural caverns penetrated by the workings are an 

 attraction to the tourist rather than of interest to the miner. The 

 extensive soughs, driven during the last century in an attempt to de-water 

 the mines, provide an abundant water suuply though in quality hardly to 

 be compared with that from the succeeding Millstone Grits, on which 

 the fame of Matlock Spa depends. 



Millstone Grit 



The scenery of the Gritstone country is in striking contrast to that of 

 the Limestone dome; heather moorland and edge-like escarpments 

 take the place of the grassy rounded forms of the limestone plateau. 



The streams of the grit-country tumble over the successive grits in a 

 succession of waterfalls and the early development of the textile industry 

 in Derbyshire was based on the water power thus provided. Moreover 

 the water from the grits is as ' soft ' as that from the limestone is ' hard ' 

 and the hydropathic hotels of Matlock and the bleachers and dyers find 

 this pure gritstone water ideal for their requirements. The Derwent 

 Valley Water Scheme has made these waters available to Sheffield, Derby, 

 Nottingham and Leicester and such a supply will prove a big factor in 

 the future development of the East Midlands. 



The so-called ' Limestone Shales ' below the Millstone grit are now 

 considered to belong to the Upper Carboniferous and rest unconformably 

 on the limestone in Derbyshire. In the shales of the Edale valley in 

 North Derbyshire, J. H. Jackson has found in descending order goniatites 

 characteristic of the lower Reticulocerus sub-zone, the Homocerus zone 

 and the upper sub-zone of Eumorphocerus but the absence of the 

 goniatite Eumorphocerus pseudo-bilingue and the associated marine 

 fossils suggests that the lower sub-zone of the Upper Carboniferous is 

 unrepresented in Derbyshire. The Edale shales are succeeded by the 

 Mam Tor sandstone and Shale Grit series or the Fifth Grit of some 

 authors, and this is followed by the Grindslow Shales which so far have 

 yielded no fossils. The Kinderscout or Fourth Grit attains its maximum 

 development in North Derbyshire and is characterised by a lower coarse 

 and often conglomeratic leaf separated by shales from a finer grained 

 and often flaggy upper division. In common with other grits the Kinder- 

 scout contains casts of plant stems usually so ill preserved as to defy 

 precise indentification. 



The Middle Grits include the Belper or Chatsworth Grit and the 

 Coxbench Grit. These grits often occur in wide courses and the Cox- 

 bench in particular has provided building stone of exceptional tensile 

 strength and weather resisting qualities. The intervening shales are seldom 

 exposed. As in the case of the Upper Kinderscout, each of these grits 

 is immediately overlain by underclay and a thin coal seam. Though 



